Chemistry Multiple Choice Questions on “Molecular Orbital Theory”.
1. Combination of two atomic orbitals results in the formation of two molecular orbitals namely _________
a) one bonding and one non-bonding orbital
b) two bonding orbitals
c) two non-bonding orbitals
d) two bonding and non-bonding orbitals
Answer: a
Clarification: F. Hund and R.F. Mullikan proposed Molecular orbital theory in the year 1932. According to this theory, the combination of two atomic orbitals results in the formation of two molecular orbitals namely one bonding and one non-bonding orbital.
2. Stability increases, as the energy ___________
a) increases
b) doesn’t change
c) decreases
d) increases and then decreases
Answer: c
Clarification: As the stability increases, the energy of that substance decreases. The higher the energy, the less stable the molecule. So stability is inversely proportional to the energy. This can be seen in any part of the universe.
3. (psi)MO = (psi)A + (psi)B.
a) True
b) False
Answer: a
Clarification: The linear combinations like additions and subtractions of wave functions of individual atomic orbitals indicate the formation of molecules mathematically, as given i.e. (psi)MO = (psi)A + (psi)B. Where (psi) represents the wavefunctions of atomic orbitals.
4. Which of the following is a condition for the combination of atomic orbitals?
a) Combining atomic orbitals need not have equal energy
b) Combining atomic orbitals must have symmetry as per molecular axis
c) Combining atomic orbitals must overlap to a minimum extent
d) For combining atomic orbitals, X-axis should be taken as a molecular axis
Answer: b
Clarification: Combining atomic orbitals must have symmetry as per molecular axis is true. The corrected statements are combining atomic orbitals must have equal energy, must overlap to the maximum extent and Z-axis should be taken as the molecular axis.
5. Sigma molecular orbitals are not symmetrical around the bonding axis.
a) True
b) False
Answer: b
Clarification: According to the nomenclature, sigma molecular orbitals are symmetrical around the bonding axis and the pi molecular orbitals are not symmetrical around the bonding axis. So the given statement is false.
6. Which of the bonding orbital has greater energy comparatively?
a) Both Bonding molecular orbital and Anti-bonding molecular orbital have the same energy
b) The energy of Bonding molecular orbital and Anti-bonding molecular orbital depends on the situation
c) Bonding molecular orbital
d) Anti-bonding molecular orbital
Answer: d
Clarification: An electron that enters bonding orbitals stabilizes the molecule as it’ in between two nuclei. Whereas when an electron is entered into the anti-bonding orbital, it needs to pull an electron away from the nucleus.
7. Take NA as the number of Anti-bonding molecular orbitals and NB as the number of Bonding molecular orbitals. The molecule is stable when NA ____________ NB.
a) is greater than
b) is equal to
c) is less than
d) is greater than or equal to
Answer: c
Clarification: When a molecule consists both bonding molecular orbitals and anti-bonding molecular orbitals, the higher the number of bonding orbitals, the more the bonding influence and the more stable the molecule will be and vice-versa.
8. What’s the bond order of Oxygen?
a) 3
b) 2
c) 1
d) 0
Answer: b
Clarification: The formula of bond order is given by 1⁄2(NB – NA) When NB is bonding orbitals and NA is the number of anti-bonding orbitals. In Oxygen, bond order = 1/2(10-6) = 2. When it’s zero the molecule cannot be formed.
9. What do you think is the relationship between bond order and bond length?
a) Directly proportional
b) Indirectly proportional
c) No relation
d) Cannot predict
Answer: b
Clarification: The bond length has defined the distance between two atoms in a molecule. The bond order depends on the bond length between two atoms in a molecule. As the bond length increases the bond decreases and vice-versa.
10. Which of the following molecule is not true about paramagnetic molecules?
a) Attracted by the magnetic field
b) A molecular orbital is singly occupied
c) An example is oxygen molecule
d) Repelled by the magnetic field
Answer: d
Clarification: Paramagnetic molecules are attracted by the magnetic field and orbitals are singly occupied. O2 is an example. Whereas diamagnetic molecules are repelled by the magnetic field, so the option is wrong.